Self-drilling, chemical bonded anchors and their utilization in mining and tunnel construction have been well-known in the art for a long time. The bonded anchor is used principally for stabilizing walls in hollow spaces such as in tunnels, galleries or the like. When constructing hollow spaces, the mechanical properties and in particular the carrying capacity of the work strata is reduced. These strata are anchored by means of the bonded anchor to more remote, undamaged rock strata and as a result are secured in the receiving material.
The setting operation of the prior art anchors is accomplished in two steps. In the first step, the anchor is drilled into the receiving material using a drilling device. The receiving material broken and reduced by the drill head of the drilled anchor at its drilling end is transported away through the exit openings arranged on the drill head and the interspace between the wall of the bore hole and the outer circumference of the anchor. In the wet drilling operation, operation, water is fed in the setting direction and the broken and reduced rock is flushed out. In the dry drilling operation, the broken down and reduced rock is suctioned off In a second step, the chemical mass is pressed out using a dispensing mechanism in the direction of the base of the bore hole, whereby the mortar mass present in the anchor moves out through the exit openings out of the anchor in the drill head into the bore hole and is distributed along the interspace between the wall of the bore hole and the external periphery of the anchor tube.
DE 100 17 750 discloses, for example, an anchor, which has an anchor tube and an inner tube arranged in the anchor tube for receiving the dispensible chemical mass. The anchor tube has a first leading end with a drill head and a second, trailing end, at which a drilling device can be coupled for rotary driving of the bonding anchor. The anchor further includes a centering device, which has at least one centering element with a radially external stop surface for co-operating with the inner surface of the anchor tube and a radially inner stop surface for co-operating with the outer surface of the receiving means, the centering element serving in the radial alignment of the receiving means in the anchor tube. The inner tube is aligned within the anchor tube by means of the centering device.
The drawback of such prior art solution is that in the drilling operation and especially during the dispensing operation, any shifts of the receiving means for the dispensible mass occurring in the anchor tube cannot be taken up by the centering device. In addition, perfect removal of the broken down and reduced stone is not possible using the prior art centering device, because the passage channels can close up during the drilling operation in the event of a shift in the axial direction of the receiving means.
DE 31 00 730 A1 describes an anchor, wherein the setting operation is effected in several single steps. After creating a bore hole with a hollow drilling rod and a drill head, for example, a tube is inserted into the bore hole. A chemical mass is introduced through the rube into the bore hole, which secures the tube in the bore hole. The drawback of this solution is the laborious setting operation, which on the one hand requires considerable logistical involvement and on the other the use of several persons.
The object of the invention is to provide an anchor, which can be set quickly and simply by the user of the drilling device and further can be used in both the wet and dry drilling operations.
According to the invention, the at least one centering element for axial support of the receiving means has stop surfaces that project at least in part into the projection of one of the ends of the receiving means.
The receiving means in the anchor tube of the anchor according to the invention is held by the at least one centering element not only in the radial direction but also in the axial direction of the anchor. In this fashion, a sufficiently large annular gap between the outer surface of the receiving means and the inner surface of the anchor tube is formed for the removal of the drilling chips produced in the dry drilling operation on the one hand or for supplying water to the drill head in the wet drilling operation, and the gap is present during the entire setting operation. On the other hand, the at least one centering element in the front region of the receiving means creates sufficient passage channels for diversion of the drilling chips from the drill head into the annular gap or for diversion of the water conducted therethrough from the annular gap into the drill head. The receiving means is no longer exposed directly to the forces occurring, which act for example from the drill head on the anchor, which results in minor damage to the receiving means and consequently reduces the susceptibility of the bonding anchor to failure. Preferably, a space is present between the leading end of the receiving means and the axial space surfaces of the at least one centering element, so that minor axial movements of the receiving means within the anchor tube can be compensated. Because the centering elements are used as single elements, they can be used also in anchors cut to length on site.
Preferably, the at least one centering element has axially attending webs for forming the radial stop surfaces and the axial stop surfaces. The webs can include fingerlike receiving means in its leading region. The webs have a length, in the event of an axial shift of the receiving means within the anchor tube and can continue to adequately hold the receiving means. Advantageously, the webs are radially expandable under axial pressure. Accordingly, the receiving means can be urged in the direction of the drill head into a receptacle formed at the insertion end of the drill head after completing the drilling operation, so that the mass dispenses by means of the pressing-out mechanism cannot flow back through the annular space between the receiving part and the anchor tube.
Preferably, the at least one centering element has at least three radial stop surfaces and three axial stop surfaces. Using at least three radial stop surfaces the guide assembly and the oriented support of the receiving means is made possible in the anchor tube.
Preferably, the radial stop surfaces and axial stop surfaces of the at least one centering element are arranged ring-shaped on a base body, wherein the base body has at least one opening. The at least one opening is preferably arranged centrally on the base part. The anchor tube has generally a circular cross-section with an inner core. The radius of the circular arrangement of the radial and axial stop surfaces corresponds approximately to the radius of the inner core of the anchor tube.
The base part is preferably formed as a disk, whose outside diameter corresponds approximately to the inside diameter of the anchor tube. At least one opening is arranged in the base part for creation of passage channels. A preferred configuration of the centering element has a ring-shaped base part, on which, perpendicular to the plane that extends through the base part, aligned webs are formed. In lieu of a disk-shaped configuration of the base part, the base part can also have a polygonal configuration.
Advantageously, the at least one centering element has, for its axial securement in the anchor tube, axial limiting surfaces. The axial limiting surfaces are arranged on the side of the base part, which are arranged with the facing side of the base part having the stop surfaces. If the at least one centering element, for example, is arranged on the setting-side end of the anchor, the centering element abuts with its axial limiting surface on the insertion end of the drill head, whereby an undesired shift of the centering element in the setting direction is prevented.
Preferably, the centering device includes two centering elements. Using two centering elements, the mounting of the receiving means in the anchor tube is made possible without additional support in the longitudinal direction. In on another embodiment, the insertion end of the drill head, for example, has a receptacle, in which the end of the receiving means lying in the setting direction of the bonding anchor is held and the other end is held aligned in the anchor tube only using one centering element.
Preferably, the at least one centering element has at least one flange stop for creating an axial limiting surface on the base part. The centering element is particularly suitable for arrangement on the second, free end of the anchor tube and is, for example, attached on that end. The outer diameter of the flange stop is preferably larger than the inner diameter of the anchor tube, whereby the axial path of the centering element is limited in the setting direction.
Preferably, for the axial securement of the at least one centering element, a retaining sleeve is provided that can cooperate with the anchor tube, whereby in the region of the second end, an outer thread is formed on the anchor tube in the region of the trailing end of the anchor tube and the retaining sleeve has an inner thread that can be brought into engagement with the outer thread on the anchor tube. The retaining sleeve preferably has a base section, which secures the at least one centering element on the second, trailing end against displacement opposite to the setting direction of the anchor. This arrangement is particularly advantageous, when the at least one centering element has a flange section as the axial limiting surface.
Advantageously, the at least one centering element is fashioned out of plastic, optionally in an injection molding process. This makes it possible to inexpensively manufacture the at least one centering element in large quantities.
Other advantageous embodiments and combinations of features of the invention will become apparent from the following detailed description and the set of patent claims.
In principle, identical parts in the Figures are provided with the same reference numbers.